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Which is correct?

The supervisor or engineers is reponsible for the project.

The supervisor or engineers are responsible for the project.
Comments  
The first sentence is the correct one, because 'or' implies that only one of them would be responsible.
If it was "supervisor or ENGINEER (singular)", then I would agree with you.

But in this case, the singular form won't do, because you can't say: "Engineers (plural) IS responsible".

In cases like this, where neither form works well, the best solution is often to rewrite the sentence to avoid the problem. E.g: "Responsibility lies with the supervisor or engineers". Now there is no verb/noun disagreement.

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Guest Which is correct?The supervisor or engineers is reponsible for the project.The supervisor or engineers are responsible for the project.
The supervisor or engineers is reponsible for the project.